A new type of fan rotor has been designed by the University of Stellenbosch specifically for the MinWaterCSP project to obtain a high design point efficiency and low noise. Measurements will be conducted to obtain the fan aerodynamic performance as well as to determine the dynamic blade loading and its interaction with the rest of the facility. In order to assess the performance of this new fan rotor with sufficient detail, Sapienza University of Rome and the University of Stellenbosch have designed and manufactured a reduced scale fan by means of rapid prototyping. The objective of this work is to estimate the discrepancies between the 1.5 m test rig and a smaller test facility.
The dimensional reduction of a test rig offers several advantages. Above all, it allows to reduce the cost of the prototype manufacturing and to investigate the flow field in proximity to the rotor, a crucial task for designers to increase robustness of the design methods. This knowledge will give designers an increased awareness on the phenomena that are involved and must be considered during the design and thus help to steadily develop more efficient fan impellers.
In a second step, the MFan blade design was readapted in order to be 3D printed. The height of each print was limited to fit the capability of the printer, in this case 140 mm, and so a single blade was printed in two separate parts. A differential infill was used for the two parts, the hub part, which was expected to be the most mechanically stressed, uses a 100% infill, while for the tip part, the infill was 25%. This guaranteed a consistent weight reduction and adequate blade stiffness. The two blade parts were assembled by means of two wooden dowel pins and glue providing excellent surface continuity between the two adjacent parts. The final assembly is shown in Figure 1.
Figure 1 – Final blade geometry (left) and half-impeller assembly (right), copyright: Sapienza and Stellenbosch University
Measurements were conducted in an experimental facility that is compliant with ISO 5801:2007, Type D, with the same procedure as described before. A sketch of the test rig is shown in Figure 2.
Figure 2 – The 630 mm test facility at Stellenbosch University, copyright: Sapienza and Stellenbosch University
The correlation between the 1.5 m experimental data and 630mm results was seen to be acceptable and minimal discrepancies can be ascribed to small geometric differences and varied installation environments.
Since performance correlation between 1.5 m and 630mm were acceptable, a flow survey in proximity of the fan impeller was undertaken. The flow investigation was made by means of a Five Holes Probe (FHP), Figure 3, a special instrument that is able, after a meticulous calibration, to read velocity and direction of the airflow.
Figure 3 – Five holes probe picture shown next to a cm scale, copyright: Sapienza and Stellenbosch University
Circumferentially averaged velocity fields at the blade outlet plane of both experimental five holes probe and CFD were compared to the profiles generated by the design code.
Some discrepancies were found between the small scale fan and the CFD in terms of flow field (see Figure 4 and Figure 5). At this stage, the reason for this is not entirely known, however, further investigations are planned, including taking flow field measurements nearer to the rotor exit as well as at the fan inlet. These investigations aim to understand the influence of inflow conditions on the flow field downstream of the fan as well as to provide a better comparison with the design data.
Figure 4 – Axial velocity profiles downstream of fan rotor, copyright: Sapienza and Stellenbosch University
Figure 5 – Tangential velocity profiles downstream of fan rotor, copyright: Sapienza and Stellenbosch University
Author of this blog is: Dr. David Volponi, Sapienza University of Rome
About Sapienza University of Rome (project partner short name: UROME)
Sapienza University, founded in 1303 by Pope Boniface VIII in Rome, is one of the oldest universities in the world and a top performer in international university rankings.
The Faculty of Engineering aims at training young engineers with an advanced education, providing them with skills in designing, planning and managing complex activities of research and development in an industrial environment. This goal is achieved by means of a broad training proposal based on advanced mathematics and physics, and professional expertise targeted to the solution of complex engineering problems concerning design of processes, plants, systems, devices and machines.
The team for Industrial Turbomachinery of Dept. of Mechanical and Aerospace Engineering works on Research and Development of Innovative solutions for industrial turbomachinery design. It works on research of new numerical strategies for aerodynamics, heat transfer, erosion, fouling and fluid-structure interaction, design, optimization and verification software for turbomachinery and big data analysis applied to turbomachinery design and operations.
For more details: https://www.uniroma1.it/it/
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